For guide bars of chain saws it is conventional to reinforce the forward region of the guide bar with a hard-metal alloy for increasing the resistance to wear at the region of the guide bar where the saw chain is turned around through an angle of 180.degree.. For this purpose, a hard metal alloy is applied to the base material of the guide bar, for example, by welding. As a coating material, cobalt hard metal alloys are used for example and are known for instance under the designation stellite 6 or stellite 12. Stellite 6 is a cobalt base alloy which includes 28 percent by weight of chromium, 4 percent by weight of tungsten and up to 1.1 percent by weight of nickel. Stellite 6 as a coating material for guide bars has up to now been effective; however, it is no longer satisfactory for all use conditions with respect to its resistance to wear and its toughness in view of the advancing development of chain saws which tend to be of higher capacity and higher rotational speed. Especially for high requirements with respect to resistance to wear, this material is too soft as a consequence of which several manufacturers have transferred to a harder material such as stellite 12 for guide bars subjected to high loading.
The material known under the designation stellite 12 is a cobalt base alloy having 29 percent by weight of chromium, 8 percent by weight of tungsten and 1.3 percent by weight of carbon. Although this material exhibits a significantly higher hardness than stellite 6, other problems occur because of the brittleness of the material which greatly affects the resistance to wear of the guide bar. Especially in a case of a saw chain which is not adequately tensioned (adequate tensioning cannot always be assured during continuous use of the chain saw), the situation can occur that the saw chain lifts off of the guide bar and impinges thereon with considerable impact when the speed of the chain is high and the cutting times are short such as when cutting off branches. Since the coating material stellite 12 has a hexagonal lattice structure, it cannot be cold formed and is therefore very brittle which can cause the coating material to break when the saw chain hits and parts thereof can break away therefrom. For this reason, stellite 12 is not suitable as a coating material for guide bars.
A further cobalt base alloy is known under the designation stellite F and includes 22 percent by weight of nickel, 12 percent by weight of tungsten, 2 percent by weight of carbon and 1 percent by weight of silicon. This alloy is not suitable as a coating material for guide bars.